The tissue distribution of clodronate (dichloromethylene bisphosphonate) in mice. The effects of vehicle and the route of administration

Is the Use of Bisphosphonates Putting Horses at Risk? An Osteoclast Perspective

Simple Summary

Bisphosphonates are a group of drugs that intervene in the bone resorption process, producing cellular death of osteoclasts. These drugs are used for skeletal conditions, such as osteoporosis in humans, and are available for veterinary medical use. Clodronate and tiludronate are bisphosphonates approved for the treatment of navicular syndrome in horses over four years old. However, these drugs are sometimes used in juvenile animals under exercise, where osteoclast activity is higher. Bisphosphonate use in juvenile and/or exercising animals could have adverse effects, including maladaptation to exercise or accumulation of microdamage. Furthermore, bisphosphonates can be bound to the skeleton for several years, resulting in a prolonged effect with no pharmaceutical reversal available. This review presents an overview of osteoclast function and a review of bisphosphonate characteristics, mechanisms of action, and side effects in order to contextualize the potential for adverse/side effects in young or exercising animals.

Abstract

Osteoclasts are unique and vital bone cells involved in bone turnover. These cells are active throughout the individual’s life and play an intricate role in growth and remodeling. However, extra-label bisphosphonate use may impair osteoclast function, which could result in skeletal microdamage and impaired healing without commonly associated pain, affecting bone remodeling, fracture healing, and growth. These effects could be heightened when administered to growing and exercising animals. Bisphosphonates (BPs) are unevenly distributed in the skeleton; blood supply and bone turnover rate determine BPs uptake in bone. Currently, there is a critical gap in scientific knowledge surrounding the biological impacts of BP use in exercising animals under two years old. This may have significant welfare ramifications for growing and exercising equids. Therefore, future research should investigate the effects of these drugs on skeletally immature horses.

Radial BMD and serum CTX-I can predict the progression of carotid plaque in rheumatoid arthritis: a 3-year prospective cohort study

OBJECTIVE

Patients with rheumatoid arthritis (RA) are almost twice as likely to develop cardiovascular disease (CVD) as those without. However, traditional CVD risks have been shown to underperform in RA patients; thus, we aimed to identify new surrogate risk factors to better reflect their atherosclerotic burden.

METHODS

A total of 380 RA patients with carotid atherosclerosis data were analyzed in this prospective cohort study. The primary outcome was carotid plaque progression over the 3-year follow-up period. Risk parameters assessed for the progression of carotid plaque were categorized as demographics, traditional CVD risks, RA-related risks, and bone parameters.

RESULTS

The progression of carotid plaque was associated with the level of rheumatoid factor (p = 0.025), serum C-terminal telopeptide of type-I collagen (CTX-I) (p = 0.014), and femur and distal radius bone mass density (BMD) (p = 0.007 and 0.004, respectively), as well as traditional CVD risk factors. In multivariable analyses, the bone parameters of serum CTX-I and distal radius BMD proved to be independent predictors of the progression of carotid plaque along with hyperlipidemia, smoking, and baseline carotid plaque (all, p < 0.05). Adding both serum CTX-I and distal radius BMD increased the carotid plaque progression prediction model's percentage of explained variance from 24 to 30%.

CONCLUSION

High serum CTX-I and lower radius BMD, reflecting high bone turnover, were independent risk factors for the progression of carotid plaque in RA patients, implicating the direct or indirect role of bone metabolism on the atherosclerotic burden.

Characterization of the small molecule ARC39, a direct and specific inhibitor of acid sphingomyelinase in vitro

Inhibition of acid sphingomyelinase (ASM), a lysosomal enzyme that catalyzes the hydrolysis of sphingomyelin into ceramide and phosphorylcholine, may serve as an investigational tool or a therapeutic intervention to control many diseases. Specific ASM inhibitors are currently not sufficiently characterized. Here, we found that 1-aminodecylidene bis-phosphonic acid (ARC39) specifically and efficiently (>90%) inhibits both lysosomal and secretory ASM in vitro. Results from investigating sphingomyelin phosphodiesterase 1 (SMPD1/Smpd1) mRNA and ASM protein levels suggested that ARC39 directly inhibits ASM's catalytic activity in cultured cells, a mechanism that differs from that of functional inhibitors of ASM. We further provide evidence that ARC39 dose- and time-dependently inhibits lysosomal ASM in intact cells, and we show that ARC39 also reduces platelet- and ASM-promoted adhesion of tumor cells. The observed toxicity of ARC39 is low at concentrations relevant for ASM inhibition in vitro, and it does not strongly alter the lysosomal compartment or induce phospholipidosis in vitro. When applied intraperitoneally in vivo, even subtoxic high doses administered short-term induced sphingomyelin accumulation only locally in the peritoneal lavage without significant accumulation in plasma, liver, spleen, or brain. These findings require further investigation with other possible chemical modifications. In conclusion, our results indicate that ARC39 potently and selectively inhibits ASM in vitro and highlight the need for developing compounds that can reach tissue concentrations sufficient for ASM inhibition in vivo.

Characterization of a new solvate of risedronate

Three new forms of the osteoporosis drug sodium risedronate, sodium [1-hydroxy-2-(3-pyridinyl)ethylidene]bisphosphonate, were identified and designated as the J, K, and M phases. Form J is an acetic acid disolvate with the chemical composition Na(+) [C(7) H(10) NO(7) P(2)](-) · 2CH(3) COOH, as determined by single-crystal structure analysis. This novel solvate is easily formed by the recrystallization of sodium risedronate from acetic acid. Dissolution of the new disolvate was characterized in distilled water, a compendial buffer, simulated gastric fluid sine pepsin (pH 1.2), and a biorelevant buffer system FaSSIF-V2 (pH 6.8). It was demonstrated that solubility of the disolvate in physiological buffers differed significantly from that of the original molecule, with delayed dissolution under simulated esophageal and gastric conditions, but rapid and complete dissolution under simulated intestinal conditions. These studies suggest that through the generation of novel solvates, the biopharmaceutical properties of poorly soluble drug candidates can be improved.

Route of administration-dependent anti-inflammatory effect of liposomal alendronate

Innate immunity and inflammation are of major importance in various pathological conditions. Intravenous (IV) and intraperitoneal (IP) liposomal alendronate (LA) treatments have been shown to deplete circulating monocytes and peritoneal macrophages resulting in the inhibition of restenosis and endometriosis (EM), respectively. Nevertheless, the correlation between the extent of circulating monocyte depletion and liposome biodistribution is unknown, and the route of administration-dependent bioactivity in restenosis and EM has not been determined. We found that, LA treatment resulted in a dose-response modified biodistribution following both IV and IP administrations. The biodistribution of high-dose LA (10mg/kg), but not that of the low-dose (1mg/kg), was similar in healthy and diseased animals. It is concluded that LA impedes its own elimination from the circulation by depleting circulating monocytes and/or inhibiting their endocytic activity, in a dose-dependent manner. Both IV and IP administration of LA mediated by the partial and transient depletion of circulating monocytes effected inhibition of restenosis. Inhibition of EM was effected only by IP administration, which depleted both intraperitoneal and circulating monocytes. Thus, EM should be considered as a local inflammatory condition with systemic manifestations as opposed to restenosis, a systemic inflammatory disease.

The role of bisphosphonates in the management of patients that have cancer

Bisphosphonates are pharmacologic agents widely used in people for managing pathologic bone resorptive conditions. Based on their physicochemical properties, bisphosphonates concentrate within areas of active bone remodeling and induce osteoclast apoptosis. Appropriate use of bisphosphonates for treating companion animals requires a thorough understanding of how bisphosphonates exert their biologic effects. This review article highlights general properties of bisphosphonates, including their pharmacology, mechanisms of action, adverse side effects, anticancer mechanisms, surrogate markers for assessing response, and potential clinical utility for treating dogs and cats diagnosed with malignant skeletal tumors.

Acute inflammatory response to endotoxin in mice and humans

Endotoxin injection has been widely used to study the acute inflammatory response. In this study, we directly compared the inflammatory responses to endotoxin in mice and humans. Escherichia coli type O113 endotoxin was prepared under identical conditions, verified to be of equal biological potency, and used for both mice and humans. The dose of endotoxin needed to induce an interleukin-6 (IL-6) concentration in plasma of approximately 1,000 pg/ml 2 h after injection was 2 ng/kg of body weight in humans and 500 ng/kg in mice. Healthy adult volunteers were injected intravenously with endotoxin, and male C57BL/6 mice (n=4 to 12) were injected intraperitoneally with endotoxin. Physiological, hematological, and cytokine responses were determined. Endotoxin induced a rapid physiological response in humans (fever, tachycardia, and slight hypotension) but not in mice. Both mice and humans exhibited lymphopenia with a nadir at 4 h and recovery by 24 h. The levels of tumor necrosis factor (TNF) and IL-6 in plasma peaked at 2 h and returned to baseline levels by 4 to 6 h. IL-1 receptor antagonist RA and TNF soluble receptor I were upregulated in both mice and humans but were upregulated more strongly in humans. Mice produced greater levels of CXC chemokines, and both mice and humans exhibited peak production at 2 h. These studies demonstrate that although differences exist and a higher endotoxin challenge is necessary in mice, there are several similarities in the inflammatory response to endotoxin in mice and humans.

Bone as an effect compartment : models for uptake and release of drugs

"Bone-seeking agents" are drugs characterised by high affinity for bone, and are disposed in bone for prolonged periods of time while maintaining remarkably low systemic concentrations. As a consequence, the bone becomes a reservoir for bone-seeking agents, and a site of both desirable and adverse effects, depending on the pharmacological activities of the specific agent. For some agents, significant systemic effects may also be produced following their prolonged release from bone, a process that is governed mostly by the rate of bone remodelling. This review covers the pharmacokinetic and pharmacodynamic features of bone-seeking agents with different pharmacological properties, including drugs (bisphosphonates, drug-bisphosphonate conjugates, radiopharmaceuticals and fluoride), bone markers (tetracycline, bone imaging agents) and toxins (lead, chromium, aluminium). In addition, drugs that do not possess bone-seeking properties but are used for therapy of bone diseases (such as antibacterials for treatment of osteomyelitis) are discussed, along with targeting of these drugs to the bone by conjugation to bone-seeking agents, local delivery systems, and other approaches. The pharmacokinetic and pharmacodynamic behaviour of bone-seeking agents is extremely complex due to heterogeneity in bone morphology and physiology. This complexity, accompanied by difficulties in human bone research caused by ethical and other limitations, gave rise to modelling approaches to study bone drug disposition. This review describes the pharmacokinetic models that have been proposed to describe the pharmacokinetic behaviour of bone-seeking agents and predict bone concentrations of these agents for different doses and patient populations. Models of different types (compartmental and physiologically based) and of different complexity have been applied, but their relevance to drug effects in the bone tissue is limited since they describe the behaviour of the "average" drug molecule. Understanding of the cellular and molecular processes responsible for the heterogeneity of bone tissue will provide better comprehension of the influence of microenvironment on drug bone disposition and the resulting pharmacological response.

Bone-Specific Drug Delivery Systems

Despite several decades of progress, bone-specific delivery is still limited by the unique anatomical features of bone, which mainly consists of inorganic hydroxyapatite. A practical approach to this problem is to produce targeted drugs that have a high affinity for hydroxyapatite. Bisphosphonates are a class of synthetic compounds structurally related to pyrophosphate. Bisphosphonates rapidly localise on the bone surface after being administered either intravenously or orally, since the P-C-P portion of the bisphosphonate structure has high affinity for hydroxyapatite. Therefore, bisphosphonate modification might be a promising method for targeting drugs selectively to the bone. Bisphosphonate-conjugated drugs are hydrophilic and highly water-soluble due to the acidic nature of the bisphosphonate moiety at physiological pH, and therefore they hardly permeate through the biological membrane of soft tissues. These physicochemical changes also reduce the intrinsic susceptibility of the drug to metabolism, promoting urinary or biliary excretion as unchanged drug. All these physicochemical and pharmacokinetic alterations contribute to the exceptional skeletal disposition of bisphosphonate-conjugated drugs. Bisphosphonate conjugation is based on chemical modification of the targeting molecule, and therapeutically optimised bisphosphonate derivatives have to be custom-developed on a case-by-case basis. The bisphosphonate moiety is usually coupled with the targeting drug through a specific linkage. The high affinity of bisphosphonate conjugates for the bone is not simply dependent on the bisphosphonate moiety but on the resultant molecule as a whole, including the linker and the linked drug. Lipophilicity (represented as log P) appears to be an appropriate index for predicting the osteotropic properties of bisphosphonate derivatives. Several strategies using bisphosphonate-conjugated drugs have been investigated at a laboratory level with the aim of obtaining therapeutically optimised treatments for conditions such as osteoporosis, osteoarthritis and bone cancer. In each case, the intention is to achieve prolonged local exposure to high concentrations of the targeting drug, thereby improving therapeutic index by enhancing pharmacological efficacy and minimising systemic adverse effects. Although most examples of bone-specific drug delivery via bone-seeking agents still remain in preclinical studies, several phosphonate-coupled radiopharmaceuticals, such as samarium-153 complexed to tetraphosphonate, are expected to be an effective pain palliation therapies for metastatic bone cancer and are currently being developed in clinical trials. Furthermore, recent reports on bisphosphonate-modified proteins have illustrated the feasibility of bone-specific delivery of biologically active protein drugs, such as cytokines and growth factors.

Mode of administration-dependent pharmacokinetics of bisphosphonates and bioavailability determination

We investigated the influence of mode of administration on the pharmacokinetics of a clinically used bisphosphonate, pamidronate, and of suberoylbisphosphonate (SuBP), a novel bisacylphosphonate of the P-CO-(C)(n)-CO-P type, in rats. Serum drug levels and tissue disposition were determined following administration of the drugs by different modes: intravenous bolus (iso-osmotic and hypo-osmotic solutions), continuous intravenous infusion, and peroral administration. Results of the study indicate that the disposition of the bisphosphonates in soft tissue (liver, kidney and spleen) was dependent on route and rate of drug administration, and on the osmoticity of the vehicle. Consequently, main pharmacokinetic parameters (AUC, CL, and V(ss)) were influenced by the mode of drug administration, precluding accurate determination of bioavailability from AUC values. On the other hand, bone and urine bisphosphonate accumulation were considerably less dependent on mode of administration, and, therefore, are recommended for bioavailability calculation.

Administration routes and delivery systems of bisphosphonates for the treatment of bone resorption

Geminal bisphosphonates (BPs) are a class of drugs considered to be stable analogs of pyrophosphate (P-O-P), a physiological regulator of calcification and bone resorption. A number of BPs have been approved for clinical use in Paget's disease, hypercalcemia of malignancy, and osteoporosis. The major disadvantage of the clinically utilized BPs is their poor oral absorption from the GI tract, typically less than 1% is absorbed. In addition, the BPs have been associated with adverse gastrointestinal effects in humans. The challenge for novel drug delivery systems is to achieve improved bioavailability and safety. In the first part of this review, we discuss the bioavailability of BPs, the effect of food on the absorption of BPs, the mechanism of BPs' absorption and the adverse gastrointestinal effects. In the second part of the review, various methods that have been used for improving the bioavailability of BPs are described. Dosage form strategies reviewed include the use of particular formulations for increasing oral absorption as well as decreasing adverse gastrointestinal effects, absorption enhancers, BP compounds and the solubility of their calcium complex/salts, and the prodrug approach. Because of the poor GI absorption, attempts have been made to enhance the bioavailability of BPs by several parenteral routes other than i.v. injections. Description of nasal administration, s.c. and i.m. injections, BP implants and targeted osteotropic delivery systems are reviewed.

Clodronate: a review of its use in breast cancer

Like other members of its class, the bisphosphonate clodronate (clodronic acid) inhibits bone resorption. The efficacy of oral clodronate 1600 mg/day in reducing the incidence of skeletal complications and metastasis development has been assessed in several clinical trials in patients with breast cancer. Long term use of oral clodronate significantly reduced the total cumulative incidence of skeletal events (including fractures, hypercalcaemia, and the need for radiotherapy for bone pain) compared with that in placebo recipients in 2 randomised double-blind placebo-controlled studies, each involving >100 patients. Significant differences in favour of clodronate were also seen in the frequency of some individual skeletal events in 1 trial. A nonblind trial in 302 patients considered to be at high risk of developing metastases found that, at a 3-year follow-up, significantly fewer patients who received clodronate for 2 years developed skeletal metastases than those in a control group. Clodronate recipients were also significantly less likely than controls to develop visceral metastases, and had significantly higher survival rates. A smaller double-blind placebo-controlled study in women with recurrent breast cancer found that clodronate significantly decreased the total number of new skeletal metastases, but not the number of patients who developed them. In a nonblind trial in 299 patients with node-positive breast cancer, however, the incidence of skeletal metastases did not differ significantly between patients who received clodronate for 3 years and those in a control group. In addition, clodronate recipients had a significantly greater incidence of nonskeletal metastases (local and visceral), and significantly lower survival rates. Intravenous or oral clodronate has been well tolerated in clinical trials. The most common adverse effects reported were mild gastrointestinal disturbances such as nausea, vomiting and diarrhoea. All these events were transient, and usually resolved without stopping treatment.

CONCLUSIONS

Clodronate is a well tolerated bisphosphonate, available in both oral and intravenous forms, that significantly reduces the incidence of skeletal complications associated with breast cancer. Further research is needed to establish more clearly its efficacy in reducing metastasis development, to assess its efficacy compared with other bisphosphonates, and to determine which patients will benefit most from treatment. Currently, clodronate is probably most effective in the treatment and prevention of general skeletal complications in patients with breast cancer.

Bisphosphonates: a review of their pharmacokinetic properties

Bisphosphonates are a unique class of drugs. As a family, they are characterized pharmacologically by their ability to inhibit bone resorption, whereas, pharmacokinetically, they are classified by their similarity in absorption, distribution, and elimination. Although all bisphosphonates have similar physicochemical properties, their antiresorbing activities differ substantially. Activity is dramatically increased when the amino group is contained in the aliphatic carbon chain. For example, alendronate, an aminobisphosphonate, is approximately 700-fold more potent than etidronate, both in vitro and in vivo. In general, bisphosphonates are poorly absorbed from the gastrointestinal tract as a result of their poor lipophilicity. In vitro and in vivo studies have shown that bisphosphonates are absorbed from the gastrointestinal tract via paracellular transport. Systemically available bisphosphonates disappear very rapidly from plasma, and are partly taken up by the bone and partly excreted by the kidney. The relative contribution of these two processes to overall plasma elimination differs significantly among bisphosphonates. To date, all bisphosphonates studied show no evidence of metabolism. Renal excretion is the only route of elimination. Studies with alendronate in rats indicate that the drug is actively secreted by an uncharacterized renal transport system, and not by the anionic or cationic renal transport systems. Bisphosphonates bind preferentially to bones which have high turnover rates, and their distribution in bone is not homogeneous. After bone uptake, the bisphosphonates are liberated again only when the bone in which they are deposited is resorbed. Thus, the half-life of bisphosphonates in bone is very long, ranging among different species from 1 to 10 years, depending largely on the rate of bone turnover.

Pharmacokinetics of clodronate in renal failure

The pharmacokinetic parameters describing the fate of one intravenous clodronate (disodium dichloromethane diphosphonate) dose was studied in 24 normal subjects and in 24 patients with different degrees of renal insufficiency. The aim of the study was to derive data for adjustment of dosage in relation to renal function. Disodium clodronate in serum and urine samples was analyzed by capillary gas chromatography with mass-selective detection. The renal clearance (CLR) of clodronate was highly dependent on renal function and declined successively with declining glomerular filtration rate (GFR). Plasma clearance (CLP) declined, too, but to a lesser degree than CLR. The impairment of renal function resulted in decreased cumulative urinary elimination of clodronate and increased total areas under the serum concentration-time curve (AUC0-infinity). Hence, as the renal elimination of clodronate diminishes with decreasing GFR, there is a related retention of the substance. As a result of the present study, the following dosages are recommended: creatinine clearance (CLCr) from 50 to 80 ml/minute, 75-100% of normal dose; CLCr 12-50 ml/minute, 50-75% of normal dose; and ClCr < 12 ml/minute, 50% of normal dose. The results must be interpreted with caution in patients with malignancy and severe skeletal disease, in whom the nonrenal clearance may vary markedly.

Effect of iron on the absorption and distribution of clodronate after oral administration in rats

The effect of iron on the absorption and distribution of disodium clodronate in rats after oral administration was studied. Disodium clodronate (300 mg/25 microCi/kg) was given both alone and with an equivalent amount of ferrous sulphate. The radioactivity in plasma and various tissue was measured. Concentration of clodronate in plasma was also determined with the GC-mass-selective detection method and the values compared with those measured with the isotope method. After administration, clodronate was rapidly cleared from plasma. Most of the dose was taken up by bone and only small amounts were found in non-calcified tissues. Concurrent ingestion of iron caused a marked decrease in the absorption of clodronate.

The effects of liposome-encapsulated and free clodronate on the growth of macrophage-like cells in vitro: the role of calcium and iron

Clodronate (dichloromethylene bisphosphonate) inhibits the activity of osteoclasts, thereby preventing bone resorption in disorders characterized by excessive bone loss. Intravenously injected clodronate encapsulated in liposomes is also known to inactivate phagocytic cells in spleen and liver in vivo. The macrophage suppressive effect of clodronate is of interest in autoimmune diseases, like rheumatoid arthritis, in which phagocytic cells are involved in inflammatory processes, but knowledge of the interaction of clodronate with phagocytic cells is scarce. We have studied the uptake of clodronate, both free and encapsulated in negatively charged liposomes, by the macrophage-like cell line RAW 264 and by other types of cell lines. The uptake was assessed by a growth inhibition assay. The liposome-encapsulated clodronate was 50 and 350 times more potent than free drug for RAW 264 and CV1-P, respectively. Cell lines with a lower endocytotic capacity were insensitive to liposome-mediated delivery of the drug. The action of free clodronate seemed to be extracellular in all cell lines studied. Calcium and/or iron have been suggested to be involved in the intracellular uptake and action of clodronate in phagocytic cells. We found that the uptake of free clodronate by RAW 264 cells was indeed mediated by calcium and iron, while the uptake of liposomal drugs was only slightly affected by calcium. The increased intracellular calcium concentration in macrophages did not significantly affect the growth-inhibitory properties of clodronate, whereas iron loading of the cells partially restored the cell growth. The data do not support the role of calcium chelation as a mechanism of action of clodronate, but suggest that intracellular iron is, at least partially involved.

Clodronate increases the calcium content in fracture callus. An experimental study in rats

Eighty-eight rats underwent intramedullary pin fixation and fracture of both tibiae. Half of the animals were given clodronate 50 mg/kg s.c. weekly. Clodronate treatment did not affect the growth of fibrocartilage or the endochondral and membranous new bone formation. The regaining of tensile load capacity of fractured bone remained unaffected by the drug. Calluses were remodeled to lamellar bone in both groups. However, although the total area invaded by mineralized tissue in callus remained unaffected by the drug, the areas of hematopoietic bone marrow tissue within mineralized callus were observed to be markedly smaller in clodronate-treated animals than in controls. The calluses in the clodronate group were significantly heavier and contained more calcium at 2 months after fracture than those in the controls.

Determination of a new bisphosphonate, YM175, in plasma, urine and bone by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic method for the determination of disodium dihydrogen(cycloheptylamino)methylene-bisphosphonate monohydrate (YM175) in plasma, urine and bone is described. Plasma obtained in high-dose animal studies is pretreated by Method A, a simple method using 1 ml of plasma, which is based on deproteinization of plasma followed by coprecipitation of the drug with calcium phosphate and removal of excess calcium ions by AG 50W-X8 resin. Plasma obtained in lower-dose clinical studies is treated by Method B, a more sensitive method using 10 ml of plasma, which is based on solid-phase extraction using a Sep-Pak C18 cartridge coupled with Method A. Urine and bone are treated similarly to Method B. The chromatographic system consists of a mobile phase at pH 11, an alkali-stable column and an electrochemical detector operating in the oxidation mode. The determination limit is 5 ng/ml for Method A and 0.5 ng/ml for Method B in plasma, 1 ng/ml in urine, and 25 ng/g in bone.

Bisphosphonates. Pharmacology and use in the treatment of tumour-induced hypercalcaemic and metastatic bone disease

The geminal bisphosphonates are a new class of drugs characterised by a P-C-P bond. Consequently, they are analogues of pyrophosphate, but are resistant to chemical and enzymatic hydrolysis. The bisphosphonates bind strongly to hydroxyapatite crystals and inhibit their formation and dissolution. This physicochemical effect leads in vivo to the prevention of soft tissue calcification and, in some instances, inhibition of normal calcification. The main effect is to inhibit bone resorption, but in contrast to the effect on mineralisation, the mechanism involved is cellular. These various effects vary greatly according to the structure of the individual bisphosphonate. The half-life of circulating bisphosphonates is very brief, in the order of minutes to hours. 20% to 50% of a given dose is taken up by the skeleton, the rest being excreted in the urine. The half-life in bone is far longer and depends upon the turnover rate of the skeleton itself. Bisphosphonates are very well tolerated; the relatively few adverse events that have been associated with their use are specific for each compound. Bisphosphonates have been used to treat various clinical conditions, namely ectopic calcification, ectopic bone formation, Paget's disease, osteoporosis and increased osteolysis of malignant origin. The three compounds commercially available for use in tumour-induced bone disease are in order of increasing potency, etidronate, clodronate and pamidronate. Most data have been obtained with the latter two agents. By inhibiting bone resorption, they correct hypercalcaemia and hypercalciuria, reduce pain, the occurrence of fractures, as well as the development of new osteolytic lesions, and in consequence improve the quality of life. In view of these actions, of their excellent tolerability and of the fact that they are active for relatively long periods, these compounds are, after rehydration, the drugs of choice in tumour-induced bone disease and an excellent auxiliary to the drugs used in oncology.

Pharmacokinetics of clodronate after single intravenous, intramuscular and subcutaneous injections in rats

The pharmacokinetics of clodronate was studied in rats after single intravenous, intramuscular and subcutaneous doses of a mixture of unlabelled and 14C-labelled disodium clodronate (25 mg/5 muCi/kg). The peak clodronate concentration in plasma was reached within 5 min., and the drug was eliminated with a half-life of about 1.5 hr regardless of administration route. Bioavailabilities after intramuscular and subcutaneous administration were 105% and 89%, respectively. During the 72 hr collection period, the mean share of clodronate recovered from the urine was about 53% of the dose regardless of administration route. Most of the drug was excreted during the first 24 hr. The amount of clodronate in bone (femur) was 186 micrograms/g tissue at 2 hr after intravenous administration, 188 micrograms/g after intramuscular administration and 157 micrograms/g after subcutaneous administration. It is concluded that absorption of clodronate after intramuscular and subcutaneous administration is rapid and good, and that the concentrations of the drug in bone after 2 hr are about the same as after intravenous administration.

Effects of clodronate and pamidronate on splenic and hepatic phagocytic cells of mice

Bisphosphonates inhibit the activity of osteoclasts and conceivably also macrophage activity. Administered in hypoosmotic solution, clodronate (dichloromethylene bisphosphonate) forms complexes with the iron of haemolysed erythrocytes and subsequently accumulates in splenic and hepatic macrophages. Pamidronate (3-amino-1-hydroxypropylidene bisphosphonate) also accumulates in the spleen and liver of mice and rats even when injected in isoosmotic solution. In the present study, the effects in mice of uncomplexed clodronate, clodronate-iron complex, clodronate-liposomes, and pamidronate on splenic and hepatic macrophages in vivo were studied by an enzyme-histochemical method. Intracellular free clodronate released in the cells after phagocytosis of clodronate-liposomes virtually eliminated all macrophages from spleen, and also Kuppfer cells from liver. Clodronate given in hypoosmotic vehicle had no effect on these cells, although it was taken up by them. Clodronate in isoosmotic vehicle, considered as uncomplexed clodronate, neither accumulates in nor affects the macrophages. Pamidronate, however, decreased the number of the cells also after isoosmotic injection. Thus, the capability of bisphosphonates to sequestrate intracellular calcium may explain their effects on macrophages.